<template>
  <div class="box">
    <div class="left">
      <el-button
        :loading="loading"
        size="mini"
        type="primary"
        @click="handleUpload"
      >点击上传</el-button>
      <div>(推荐<span class="red">下载模板文件</span>，填写后上传)</div>
      <div class="red">点击查看文件上传要求</div>
    </div>
    <div class="right">
      <input
        ref="excel-upload-input"
        class="excel-upload-input"
        type="file"
        accept=".xlsx, .xls"
        @change="handleClick"
      >
      <div
        class="drop"
        @drop="handleDrop"
        @dragover="handleDragover"
        @dragenter="handleDragover"
      >
        <i class="el-icon-upload icon" />
        <p class="text">将文件拖到此处</p>
      </div>
    </div>
  </div>
</template>

<script>
import XLSX from 'xlsx'

export default {
  name: 'ReadExcel',
  props: {
    beforeUpload: Function, // eslint-disable-line
    onSuccess: Function // eslint-disable-line
  },
  data() {
    return {
      loading: false,
      excelData: {
        header: null,
        results: null
      }
    }
  },
  methods: {
    generateData({ header, results }) {
      this.excelData.header = header
      this.excelData.results = results
      this.onSuccess && this.onSuccess(this.excelData)
    },
    handleDrop(e) {
      e.stopPropagation()
      e.preventDefault()
      if (this.loading) return
      const files = e.dataTransfer.files
      if (files.length !== 1) {
        this.$message.error('Only support uploading one file!')
        return
      }
      const rawFile = files[0] // only use files[0]

      if (!this.isExcel(rawFile)) {
        this.$message.error(
          'Only supports upload .xlsx, .xls, .csv suffix files'
        )
        return false
      }
      this.upload(rawFile)
      e.stopPropagation()
      e.preventDefault()
    },
    handleDragover(e) {
      e.stopPropagation()
      e.preventDefault()
      e.dataTransfer.dropEffect = 'copy'
    },
    handleUpload() {
      this.$refs['excel-upload-input'].click()
    },
    handleClick(e) {
      const files = e.target.files
      const rawFile = files[0] // only use files[0]
      if (!rawFile) return
      this.upload(rawFile)
    },
    upload(rawFile) {
      this.$refs['excel-upload-input'].value = null // fix can't select the same excel

      if (!this.beforeUpload) {
        this.readerData(rawFile)
        return
      }
      const before = this.beforeUpload(rawFile)
      if (before) {
        this.readerData(rawFile)
      }
    },
    readerData(rawFile) {
      this.loading = true
      return new Promise((resolve, reject) => {
        const reader = new FileReader()
        reader.onload = (e) => {
          const data = e.target.result
          const workbook = XLSX.read(data, { type: 'array' })
          const firstSheetName = workbook.SheetNames[0]
          const worksheet = workbook.Sheets[firstSheetName]
          const header = this.getHeaderRow(worksheet)
          const results = XLSX.utils.sheet_to_json(worksheet)
          this.generateData({ header, results })
          this.loading = false
          resolve()
        }
        reader.readAsArrayBuffer(rawFile)
      })
    },
    getHeaderRow(sheet) {
      const headers = []
      const range = XLSX.utils.decode_range(sheet['!ref'])
      let C
      const R = range.s.r
      /* start in the first row */
      for (C = range.s.c; C <= range.e.c; ++C) {
        /* walk every column in the range */
        const cell = sheet[XLSX.utils.encode_cell({ c: C, r: R })]
        /* find the cell in the first row */
        let hdr = 'UNKNOWN ' + C // <-- replace with your desired default
        if (cell && cell.t) hdr = XLSX.utils.format_cell(cell)
        headers.push(hdr)
      }
      return headers
    },
    isExcel(file) {
      return /\.(xlsx|xls|csv)$/.test(file.name)
    }
  }
}
</script>

<style lang="scss" scoped>
.excel-upload-input {
  display: none;
  z-index: -9999;
}
.box {
  display: flex;
  width: 700px;
  height: 200px;
  margin: 100px auto;
  border: 1px dashed #ccc;
  .left {
    display: flex;
    flex-direction: column;
    justify-content: center;
    align-items: center;
    flex: 1;
    border-right: 1px dashed #ccc;
  }
  .right {
    display: flex;
    flex-direction: column;
    justify-content: center;
    align-items: center;
    flex: 1;
  }
  .red {
    color: red;
  }
  .el-button {
    margin-bottom: 10px;
  }
  .text {
    color: #999;
  }
  .icon {
    font-size: 80px;
    color: #ccc;
  }
}
</style>
